The event, from October 8 to 11, is being attended by Portuguese government officials, NATO representatives, defence experts, legislators from the 30 NATO member states and representatives of the alliance's partner countries, reports Xinhua news agency.
The participants are also scheduled to assess NATO's relations with Russia and China, and the situation in the Middle East and North Africa.
They will discuss global action on climate change and the fight against "misinformation" about the pandemic.
Gerald Connolly, president of the NATO Parliamentary Assembly, described Portugal as a "crucial partner" in the revision of the alliance's strategic concept.
Ruxandra Popa, secretary general of the NATO Parliamentary Assembly, said that the session's resolutions "will be sent to the secretary general of NATO and to the governments of the member countries".